U.S. patent application number 12/598097 was filed with the patent office on 2010-05-13 for high reduction combined planetary gear mechanism.
Invention is credited to Hitoshi Maekawa.
Application Number | 20100120574 12/598097 |
Document ID | / |
Family ID | 39943330 |
Filed Date | 2010-05-13 |
United States Patent
Application |
20100120574 |
Kind Code |
A1 |
Maekawa; Hitoshi |
May 13, 2010 |
HIGH REDUCTION COMBINED PLANETARY GEAR MECHANISM
Abstract
A high reduction combined planetary gear mechanism includes an
input shaft (2), an output shaft (3), a first planetary gear
mechanism (4), and a second planetary gear mechanism (5). The first
planetary gear mechanism (4) includes a first sun gear (6) of which
the center is coupled to the input shaft (2), a first internal gear
(7), and a first planetary gear (8). A first support shaft (9) for
rotatably supporting the first planetary gear (8) is fixed to a
first carrier (10), and the output shaft (3) is fixed to the center
of the first carrier (10). The second planetary gear mechanism (5)
includes a second sun gear (11) of which the center is coupled to
the input shaft (2), a second internal gear (12), and a second
planetary gear (13). A second support shaft (14) for rotatably
supporting the second planetary gear (13) is fixed to a stationary
frame. The first internal gear (7) and the second internal gear
(12) are formed on the inner peripheral surface of a rotatable
common annular frame (16). The annular frame (16) is rotatably
mounted on the input shaft (2).
Inventors: |
Maekawa; Hitoshi;
(Tsukuba-shi, JP) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
US
|
Family ID: |
39943330 |
Appl. No.: |
12/598097 |
Filed: |
March 11, 2008 |
PCT Filed: |
March 11, 2008 |
PCT NO: |
PCT/JP2008/054415 |
371 Date: |
October 29, 2009 |
Current U.S.
Class: |
475/331 |
Current CPC
Class: |
F16H 1/46 20130101 |
Class at
Publication: |
475/331 |
International
Class: |
F16H 1/46 20060101
F16H001/46 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2007 |
JP |
2007-121621 |
Claims
1. A high reduction combined planetary gear mechanism comprising a
plurality of planetary gear mechanisms, wherein planetary gears
included in at least one planetary gear mechanism of the plurality
of planetary gear mechanisms are non-axisymmetrically arranged to
expand the flexibility in design.
2. A high reduction combined planetary gear mechanism comprising a
plurality of planetary gear mechanisms, wherein only a planetary
gear mechanism in which a carrier does not rotate among the
plurality of planetary gear mechanisms is non-axisymmetrically
arranged.
3. A high reduction combined planetary gear mechanism comprising an
input shaft, an output shaft, a first planetary gear mechanism, and
a second planetary gear mechanism, wherein the first planetary gear
mechanism includes a first sun gear of which the center is coupled
to the input shaft, a first internal gear, and first planetary
gears, first support shafts for rotatably supporting the first
planetary gears are fixed to a carrier, and the output shaft is
fixed to the center of the carrier, wherein the second planetary
gear mechanism includes a second sun gear of which the center is
coupled to the input shaft, a second internal gear, and second
planetary gears, and second support shafts for rotatably supporting
the second planetary gears are fixed to a stationary frame, wherein
the first internal gear and the second internal gear are formed on
the inner peripheral surface of a rotatable common annular frame,
and the annular frame is rotatably mounted on the input shaft.
4. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to a high reduction combined
planetary gear mechanism in which the flexibility in design is
expanded.
BACKGROUND ART
[0002] Conventionally, a planetary gear mechanism including a sun
gear, planetary gears, an internal gear, and a carrier holding
planetary gears is widely applied to a drive system of a mechanical
system due to the following excellent features.
[0003] (1) Realization of a high reduction ratio is possible
[0004] (2) The mechanism is compact with respect to its reduction
ratio and transmission torque.
[0005] (3) A coaxial arrangement of input and output is
possible
[0006] Conventionally, a combined planetary gear mechanism obtained
by coupling respective elements of a plurality of planetary gear
mechanisms is known, and the combined planetary gear mechanism
realizes a high reduction ratio which cannot be realized by a
single planetary gear mechanism.
[0007] However, in the conventional planetary gear mechanism, the
reduction ratio which can be realized by the single planetary gear
mechanism is about 1/4 to 1/10, various conditions are imposed on a
design, and the flexibility in selection of the number of teeth of
a gear or the reduction ratio is unexpectedly small.
[0008] That is, since various conditions (geometric conditions,
contiguity conditions, assembly conditions, etc.) are imposed on
the design of the planetary gear mechanism, the flexibility in
design is remarkably constrained. Especially, the assembly
conditions that all planetary gears mesh with a sun gear and an
internal gear correctly are extremely severe constraints, and the
combinations of the number of teeth and reduction ratio which can
be selected is significantly limited.
[0009] For example, in a case where three planetary gears are
arranged at intervals of 120.degree., out of six combination
candidates for the number of teeth, only one can be selected (refer
to FIG. 4).
[0010] Meanwhile, although it is generally premised that the
planetary gears are axisymmetrically arranged at regular intervals
in the design of the planetary gear mechanism, this premise
actually becomes a reason for the extremely severe constraints
being applied as the assembly conditions. On the other hand, if a
slight non-axisymmetrical arrangement of the planetary gears is
permitted, the assembly conditions are excluded, and the
flexibility in design can be significantly expanded.
[0011] For example, a configuration in which at least one planetary
gear is arranged at a central angle position different from other
planetary gears is known (refer to Patent Document 1). That is, the
technique itself for arranging the planetary gears
non-axisymmetrically to expand the flexibility in design is
well-known.
[0012] For example, if three planetary gears are permitted to be
arranged at angles other than 120.degree., out of two combination
candidates for the number of teeth, one can be selected, and the
flexibility in design is expanded by 3 times (when this is
generalized, the flexibility in design become N.sub.p times the
number of planetary gears).
[0013] [Patent Document 1] Japanese Patent Examined Publication No.
S38-12866
DISCLOSURE OF THE INVENTION
Problem that the Invention is to solve
[0014] However, when the planetary gears are non-axisymmetrically
arranged, the total acting force between the gears does not become
zero, and an unbalanced force is generated. Since this unbalanced
force is revolved at the same speed of the rotation of the carrier,
this causes noise and vibration depending on the applications and
conditions of use of the planetary gear mechanism.
[0015] The object of the present invention is to solve the above
conventional problems, and realize a high reduction combined
planetary gear mechanism with high flexibility, and a reduced
unbalanced force with only a small amount of noise and
vibration.
Means for Solving the Problems
[0016] In order to achieve the above object, the present invention
provides a high reduction combined planetary gear mechanism
including a plurality of planetary gear mechanisms. Planetary gears
of at least one planetary gear mechanism of the plurality of
planetary gear mechanisms are non-axisymmetrically arranged to
expand the flexibility in design.
[0017] In order to achieve the above object, the present invention
provides a high reduction combined planetary gear mechanism
including a plurality of planetary gear mechanisms, wherein only a
planetary gear mechanism in which a carrier does not rotate among
the plurality of planetary gear mechanisms is non-axisymmetrically
arranged.
[0018] In order to achieve the above object, the present invention
provides a high reduction combined planetary gear mechanism
including an input shaft, an output shaft, a first planetary gear
mechanism, and a second planetary gear mechanism. The first
planetary gear mechanism includes a first sun gear of which the
center is coupled to the input shaft, a first internal gear, and a
first planetary gears, first support shafts for rotatably
supporting the first planetary gears are fixed to a carrier, and
the output shaft is fixed to the center of the carrier. The second
planetary gear mechanism includes a second sun gear of which the
center is coupled to the input shaft, a second internal gear, and
second planetary gears, and second support shafts for rotatably
supporting the second planetary gears are fixed to a stationary
frame. The first internal gear and the second internal gear are
formed on the inner peripheral surface of a rotatable common
annular frame, and the annular frame is rotatably mounted on the
input shaft.
[0019] The high reduction combined planetary gear mechanism of
claim 3, wherein planetary gears of either or both of the first
planetary gear mechanism and the second planetary gear mechanism
are non-axisymmetrically arranged.
Advantage of the Invention
[0020] According to the high reduction combined planetary gear
mechanism related to the present invention, the following effects
are obtained.
[0021] (1) Flexibility in selecting the number of teeth of the
combined planetary gear mechanism can be expanded to N.sub.p (the
number of planetary gears) times.
[0022] (2) A high reduction ratio of N.sub.p times a conventional
design can be realized.
[0023] (3) The use of a high-cost internal gear can be suppressed
to a minimum.
[0024] (4) High-cost shifted gears are unnecessary, and only
standard gears can be used.
[0025] (5) An unbalanced force is not revolved dynamically and
vibration noises are not generated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a conceptual diagram illustrating an embodiment of
the present invention.
[0027] FIG. 2 is a perspective view illustrating the embodiment of
the present invention.
[0028] FIG. 3 is a perspective view illustrating the embodiment of
the present invention.
[0029] FIG. 4 is a table showing the propriety of the combination
of a planetary gear mechanism.
[0030] FIG. 5 shows views illustrating problems and improvements by
the combination of the planetary gear mechanism.
DESCRIPTION OF REFERENCE NUMERALS AND SIGNS
[0031] 1: HIGH REDUCTION COMBINED PLANETARY GEAR MECHANISM
[0032] 2: INPUT SHAFT
[0033] 3: OUTPUT SHAFT
[0034] 4: FIRST PLANETARY GEAR MECHANISM
[0035] 5: SECOND PLANETARY GEAR MECHANISM
[0036] 6: FIRST SUN GEAR
[0037] 7: FIRST INTERNAL GEAR
[0038] 9: FIRST SUPPORT SHAFT
[0039] 10 FIRST CARRIER
[0040] 11: SECOND SUN GEAR
[0041] 12: SECOND INTERNAL GEAR
[0042] 13: SECOND PLANETARY GEAR
[0043] 14: SECOND SUPPORT SHAFT
[0044] 15: SECOND CARRIER
[0045] 16: ANNULAR FRAME
BEST MODE FOR CARRYING OUT THE INVENTION
[0046] The best mode for carrying out a high reduction combined
planetary gear mechanism according to the present invention will be
described below with reference to the drawings on the basis of an
embodiment.
Embodiment
[0047] FIGS. 1 to 3 are views illustrating the embodiment of the
high reduction combined planetary gear mechanism according to the
present invention. The high reduction combined planetary gear
mechanism 1 includes an input shaft 2, an output shaft 3, a first
planetary gear mechanism 4, hand a second planetary gear mechanism
5.
[0048] The first planetary gear mechanism 4 has a first sun gear 6
of which the center is coupled to the input shaft 2, a first
internal gear 7, and a first planetary gear 8, and a first support
shaft 9 which rotatably supports the first planetary gear 8 is
fixed to the first carrier 10. The output shaft 3 is fixed to the
center of the first carrier 10.
[0049] The second planetary gear mechanism 5 has a second sun gear
11 of which the center is coupled to the input shaft 2, a second
internal gear 12 and a second planetary gear 13, the second support
shaft 14 which rotates with the second planetary gear 13 is
rotatably supported by a second carrier 15, and the second carrier
15 is fixed to a stationary frame which is not shown.
[0050] The high reduction combined planetary gear mechanism 1
according to the present invention is obtained by coupling the
first planetary gear mechanism 4 and the second planetary gear
mechanism 5 as follows as a configuration which obtains a high
reduction ratio. That is, the first internal gear 7 and the second
internal gear 12 are formed in the inner peripheral surface of a
rotatable common annular frame 16. The annular frame 16 is
rotatably mounted on the input shaft 2, as shown in FIG. 1. A
configuration which is pivoted on the input shaft 2 is omitted in
FIGS. 2 and 3.
[0051] By adopting the above configuration, the high reduction
combined planetary gear mechanism according to the present
invention exhibits the following functions.
[0052] Before that, the formulation in an independent planetary
gear will be described. In using the planetary gear, input is given
to two elements among the three elements of a sun gear, a carrier,
and an internal gear, and output is taken out from the remaining
one element, and the speed relationship of these three elements is
defined by the following Formulas 1 and 2.
[ Formula 1 ] .omega. s - .alpha. .omega. c + ( .alpha. - 1 )
.omega. i = 0 ( 1 ) [ Formula 2 ] .alpha. = 1 + Z i Z s ( 2 )
##EQU00001##
[0053] .omega..sub.s: Sun gear speed
[0054] Z.sub.s: Number of teeth of sun gears
[0055] .omega..sub.c: Carrier speed
[0056] .omega..sub.i: Internal gear speed
[0057] Z.sub.i: Number of teeth of internal gears
[0058] A general planetary gear is used as a reducer in which the
internal gear is fixed, input is made from the sun gear, and output
is made from the carrier is performed. This is equivalent to adding
a constraint condition to Formula 1, and speed relationship changes
as in the following Formula 3.
[ Formula 3 ] .omega. c = 1 .alpha. .omega. s ( 3 )
##EQU00002##
[0059] Next, it can be considered that the internal gear is not
fixed, but rotates actively in a direction opposite to the rotation
of the carrier. Then, since a portion of the rotation of the
carrier is cancelled by the reverse rotation of the internal gear,
the speed of the carrier becomes smaller than that of Formula (3),
and a high reduction ratio can be obtained. Thus, the relationship
of the following Formula 4 is introduced into the speed of the sun
gear and the internal gear.
[ Formula 4 ] .omega. i = - 1 .beta. .omega. s ( 4 )
##EQU00003##
[0060] When the constraint of Formula 4 is added to Formula 1, the
reduction ratio .gamma. from the sun gear to the carrier can be
derived as the following Formulas 5 and 6.
[ Formula 5 ] .omega. c = 1 .gamma. .omega. s ( 5 ) [ Formula 6 ]
.gamma. = .alpha. .beta. 1 - .alpha. + .beta. ( 6 )
##EQU00004##
[0061] It can be understood from Formula 6 that a very high
reduction ratio is obtained in the case of
1-.alpha.+.beta..apprxeq.0. In addition, the limit of
.beta..fwdarw..varies. is equivalent to a state where the internal
gear is fixed. At that time, Formulas 3 and 5 coincide with each
other.
[0062] The high reduction combined planetary gear mechanism
according to the present invention will be described with reference
to the formulation in the above independent planetary gear. Here,
as for the first planetary gear mechanism 4, the number of teeth of
the first sun gear 6 is defined as Z.sub.s1, the number of teeth of
the first internal gear 7 is defined as Z.sub.i1, the number of
teeth of the second sun gear 11 is defined as Z.sub.s2, and the
number of teeth of the second internal gear 12 is defined as
Z.sub.s2.
[0063] Then, the first planetary gear mechanism 4 is equivalent to
the above independent planetary gear mechanism, and the internal
gear thereof is rotated by the second planetary gear mechanism 5.
Here, on the basis of Formulas 2 and 6, the speed ratios .alpha.
and .beta. which appear in formulation can be expressed as the
following Formulas 7 to 9 according to the number of teeth of each
gear.
[ Formula 7 ] .alpha. = 1 + Z i 1 Z s 1 ( 7 ) [ Formula 8 ] .beta.
= Z i 2 Z s 2 ( 8 ) [ Formula 9 ] .gamma. = Z i 2 ( Z s 1 + Z i 1 )
Z s 1 Z i 2 - Z s 2 Z i 1 ( 9 ) ##EQU00005##
[0064] Moreover, in order to simplify a mechanism, when the number
of teeth of the first internal gear 7 and the number of teeth of
the second internal gear 12 are made equal to each other, the
reduction ratio .gamma. expressed by Formula 9 can be modified as a
reduction-ratio .gamma.' expressed by the following Formula 10.
[ Formula 10 ] .gamma. ' = Z s 1 + Z i 1 Z s 1 - Z s 2 ( 10 )
##EQU00006##
[0065] Here, Formulas 9 and 10 show the reduction ratios of the
combined planetary gear mechanism, and when the denominators
thereof are brought close to zero, high reduction ratios are
obtained. This is equivalent to reducing the difference in number
of teeth between the first sun gear 6 of the first planetary gear
mechanism 4 and the second sun gear 11 of the second planetary gear
mechanism 5 in Formula 10. Additionally, the same direction
(Z.sub.s1>Z.sub.s2, .gamma.'>0) or opposite direction
(Z.sub.s1<Z.sub.s2, .gamma.'<0) of input/output rotation can
be set depending on the magnitude relation of the numbers of teeth
of the first and second sun gears.
[0066] As described above, in the high reduction combined planetary
gear mechanism 1 according to the present invention, the function
that a high reduction ratio is obtained can be exhibited by
appropriately setting the difference in number of teeth between the
first sun gear 6 of the first planetary gear mechanism 4 and the
second sun gear 11 of the second planetary gear mechanism 5.
[0067] As a feature of the high reduction combined planetary gear
mechanism according to the present invention, there is the
extremely remarkable effect that the assembly conditions of the
planetary gear are relaxed. This point will be described below.
[0068] In the conventional planetary gear design, although N.sub.p
planetary gears are axisymmetrically arranged at regular intervals
on a carrier, all the planetary gears need to correctly mesh with a
sun gear and an internal gear. This assembly condition is expressed
by the following Formula 11 by the numbers of teeth Z.sub.s of the
sun gear and the numbers of teeth Z.sub.i of the internal gear.
[Formula 11]
Z.sub.s+Z.sub.i=MN.sub.p (11)
[0069] M: Arbitrary integer
[0070] N.sub.p: Number of planetary gears
[0071] Z.sub.s, Z.sub.i: Both are even numbers or odd numbers
[0072] However, although the combination of the numbers of teeth
which can be selected by Formula 11 have already been described,
the combination is remarkably limited, and the number of teeth of a
sun gear which can be selected with respect to the number of teeth
of a certain internal gear is only one out of 2N.sub.p ways, and
the planetary gear cannot be correctly assembled in the remaining
2N.sub.p-1 ways (refer to FIG. 4).
[0073] On the other hand, according to the high reduction combined
planetary gear mechanism related to the present invention, if a
slight non-axisymmetrical arrangement of the planetary gear is
permitted, assembly conditions can be significantly relaxed, and
the number of teeth which can be selected can be expanded to one
out of two ways. For example, when the number of the planetary
gears is N.sub.p=3 in both the first and second planetary gear
mechanisms 4 and 5, only 1/6 can conventionally be selected from
the candidates of the number of teeth, whereas one half of the
candidates can be selected if the assembly conditions are relaxed.
The concrete process of the relaxation of the assembly conditions
will be shown below.
[0074] In addition, which one out of the numbers of teeth of the
first planetary gear mechanism 4 and the second planetary gear
mechanism is first determined is not particularly limited. Here,
when the noise vibration caused by an unbalanced force becomes a
problem, it is preferable to first determine the number of teeth of
the first planetary gear mechanism 4 so that the first planetary
gear mechanism 4 is axisymmetrically arranged, and to determine the
second planetary gear mechanism 5 accordingly.
[0075] (1) As shown in the following Formula 12, the integer
quotient M and remainder .DELTA.M are obtained by dividing the sum
Z.sub.s+Z.sub.i of the numbers of teeth by N.sub.p.
[Formula 12]
Z.sub.s+Z.sub.i=MN.sub.p+.DELTA.M(1.ltoreq..DELTA.M.ltoreq.N.sub.p-1)
(12)
[0076] Here, if the remainder is zero (this applies to the first
planetary gear mechanism 4 in this example), planetary gears may be
axisymmetrically arranged at regular intervals, and the subsequent
process is unnecessary. Here, if the remainder is not zero (this
applies to the second planetary gear mechanism in this example),
the non-axisymmetrical arrangement of the planetary gears is
necessary, and the subsequent process proceeds.
[0077] (2) As shown in the following Formula 13, an integer
M.sub.k(1.ltoreq.k.ltoreq.N.sub.p) equivalent to the arrangement
interval of the planetary gears is determined, and M.sub.k
corresponding to .DELTA.M.sub.k=1 and .DELTA.M.sub.k=0 is
distributed as uniformly as possible. This is equivalent to
uniformly distributing the remainder of Formula 12, thereby
minimizing the asymmetry of the arrangement of the planetary
gears.
[Formula 13]
M.sub.k=M+.DELTA.M.sub.k (13)
.DELTA.M.sub.k=1(.DELTA.M places of N.sub.p places)
.DELTA.M.sub.k=0(N.sub.p-.DELTA.M places of N.sub.p places)
[0078] (3) Planetary gears may be arranged on a carrier in an
interval ratio of M.sub.1:M.sub.2: . . . MN.sub.p. Here, " interval
ratio of M.sub.1:M.sub.2: . . . MN.sub.p" is as follows, for
example, when being based on the first planetary gear mechanism 4
and the second planetary gear mechanism in the embodiment
[0079] <As for First Planetary Gear Mechanism 4>
[0080] Division of Formula 12: (50+100)/3=50; Remainder=0
[0081] Can be axisymmetrically arranged since the formula can be
divided
[0082] Interval ratio 1:1:1
[0083] <As for Second Planetary Gear Mechanism>
[0084] Division of Formula 12: (48+100)/3=49; Remainder=1
[0085] Can be non-axisymmetrically arranged since there is a
remainder.
[0086] Interval ratio 49:49:49+1=49:49:50
[0087] (Configuration Example)
[0088] A concrete example of the high reduction combined planetary
gear mechanism according to the present invention will be described
below. The number N.sub.p=3 of the planetary gears and the internal
gear are the same (Z.sub.i2=Z.sub.i1) in the first planetary gear
mechanism 4 and the second planetary gear mechanism 5.
[0089] The number of teeth of the first planetary gear mechanism 4
aims at obtaining a positive reduction ratio which is as large as
possible under the condition where the sun gear Z.sub.s1=50 and the
internal gear Z.sub.i1=100. Since the first planetary gear 8 of the
first planetary gear mechanism 4 satisfies the assembly conditions
of Formula 11, the first planetary gears can be axisymmetrically
arranged at regular intervals of 120.degree..
[0090] If the number of teeth Z.sub.s2 of the second sun gear of
the second planetary gear mechanism 5 satisfies the following
condition in Formula 10, a positive high reduction ratio can be
obtained.
Z.sub.s2.apprxeq.Z.sub.s1
Z.sub.s2<Z.sub.s1
Z.sub.s2 is the same even number as Z.sub.i2=100
[0091] In this case, the number of teeth which satisfies the above
condition in the immediate vicinity of the Z.sub.s1=50 is
Z.sub.s2=48, and a high reduction ratio of .gamma.'=75 can be
obtained.
[0092] However, since the number of teeth (the number of teeth of
the sun gear Z.sub.s2=48, and the number of teeth of the internal
gear Z.sub.i2=100) of the second planetary gear mechanism 5 does
not satisfy the assembly conditions of the above Formula 11, the
sun gear and the planetary gear interfere with each other in a
region shown by an arrow in FIG. 5A. Then, when the
non-axisymmetrical arrangement is permitted and the assembly
conditions are relaxed along the above process, all the planetary
gears can be correctly assembled in FIG. 5B.
[0093] On the other hand, when the planetary gears are
axisymmetrically arranged without relaxing the assembly conditions,
the number of teeth which satisfies the assembly conditions in the
intermediate vicinity of the Z.sub.s1=50 becomes Z.sub.s2=44, and
the reduction ratio .gamma.' obtained will decrease to 25 which is
one third of the aforementioned value.
[0094] The quantitative evaluation when the planetary gears have
the above asymmetry is as follows.
[0095] Arrangement interval of planetary gears: interval ratio
49:49:50
[0096] Geometric unsymmetrical amount: (Moving distance of
planetary gear shaft from axisymmetrical position) [0097] 0.52
times as large as gear module [0098] 2.0% of diameter of planetary
gear (number of teeth 26)
[0099] Mechanical unsymmetrical amount: 0.82%
[0100] |Unbalanced force|/(Number of planetary gears.times.|Acting
force between planetary gear and sun gear|)
[0101] In addition, the mechanical unsymmetrical amount is defined
as |Unbalanced force|/(Number of planetary gears.times.|Acting
force between planetary gear and sun gear|). When the value of the
mechanical unsymmetrical amount is calculated in this embodiment,
the value becomes 0.82%.
[0102] As for the asymmetry of the high reduction combined
planetary gear mechanism according to the present invention, the
expansion of the flexibility in design, and high reduction ratio
may be suitably adopted by taking into consideration conditions,
such as the intended purpose and conditions of use of the combined
planetary gear mechanism.
[0103] As described above, according to the high reduction combined
planetary gear mechanism related to the present invention, the
assembly conditions can be relaxed, and the following remarkable
effects are obtained.
[0104] (1) Realization of high reduction ratio
[0105] A high reduction ratio, N.sub.p times a conventional design
where the assembly conditions are not relaxed, can be obtained.
[0106] (2) Only one internal gear is used
[0107] Even when the assembly conditions are not relaxed, the
reduction ratio of, for example, .gamma.=97 is obtained with the
numbers of teeth including Z.sub.s1=50, Z.sub.i1=100, Z.sub.s2=47,
and Z.sub.i2=97. In this case, however, two kinds of internal gears
having different numbers of teeth are required.
[0108] However, generally, compared with the external gear, the
internal gear is manufactured with difficulty, and high costs, and
is also limited in the selection of the number of teeth. On the
other hand, according to the present invention, since the numbers
of teeth of two internal gears are equal to each other, one
internal gear can be shared in an actual mechanism.
[0109] (3) Unbalanced force is not revolved dynamically.
[0110] As a result of arranging planetary gears
non-axisymmetrically, the total of an acting force in a place where
the sun gear and the planetary gears contact each other does not
become zero, but a radial unbalanced force is generated. Since this
unbalanced force is revolved at the same speed as the rotation of
the carrier, there is a possibility that noise and vibration will
be generated. However, according to the present invention, since
the carrier of the second planetary gear mechanism is fixed,
unbalanced force is not revolved. That is, if the first planetary
gear mechanism has an axisymmetrical arrangement and the second
planetary gear mechanism has a non-axisymmetrical arrangement, even
if the assembly conditions are relaxed, the direction of the
unbalanced force is constant, and noise and vibrations are not
generated.
[0111] Although the best mode for carrying out the high reduction
combined planetary gear mechanism according to the present
invention has been described above on the basis of the embodiment,
it is needless to say that the present invention is not limited to
such an embodiment, and there are various embodiments within the
range of technical matters set forth in the claims.
* * * * *